178 SLODIES HOR STLODLENAGS: 
rock. After an abundant fall of rain or when the snow melts in 
the spring, the cracks, crevices and pores in the rocks cannot 
carry away the water nearly as rapidly as it collects in these pas- 
sages at or near the surface. If the temperature at such a time 
is fluctuating between freezing and thawing, the water will be 
alternating in a liquid and solid state. As the water congeals 
again and again the walls are pressed farther and farther apart. 
The ice acts as a wedge which automatically adjusts itself to the 
size of the crack, until the opening is sufficiently wide and deep 
to allow the free passage of the water. Not only are the cracks 
and crevices very much enlarged and extended through the stres- 
ses exerted by the solidification of the water but the stone is in 
itself materially weakened. 
The danger from the freezing of water collected along part- 
ing planes must not be confused with the danger attendant upon 
the freezing of water which fills the pores of the rock. The com- 
pact, thoroughly homogenous rocks, without bedding or other 
parting planes, whether sedimentary or igneous, are in less dan- 
ger from alternate freezing and thawing than those in which 
these structures occur. 
Alternate freezing and thawing of the included water has 
been one of the most potent causes for the decay of building 
stone, more especially that stone which is bedded or otherwise 
laminated. The most disastrous results occasionally occur from 
using stone which has not been properly seasoned, and in cases 
where the stone has been laid on edge instead of on the bed. 
In the first case the stone is materially weakened throughout 
by freezing, while in the latter exfoliation or scaling is liable to 
ensue. The most trying place in a building, in which to place 
a stone, is at the ‘‘ water line,’ where saturation is most common 
and the greatest alternations of freezing and thawing occur. The 
conditions are more severe in the case of bridge abutments and 
retaining walls than elsewhere. In bridge abutments the courses 
of stone at the level of the water are often badly shelled and 
broken, while the stone above and below is scarcely injured. It 
is not uncommon to observe all the courses of a retaining wall 
